Constraints on the Production of Phosphine by Venusian Volcanoes

Abstract

The initial reports of the presence of phosphine in the cloud decks of Venus have led to the suggestion that volcanism is the source of phosphine, through volcanic phosphides ejected into the clouds. Here, we examine the idea that mantle plume volcanism, bringing material from the deep mantle to the surface, could generate observed amounts of phosphine through the interaction of explosively erupted phosphide with sulfuric acid clouds. The direct eruption of deep mantle phosphide is unphysical, but a shallower material could contain traces of phosphide, and could be erupted to the surface. The explosive eruption that efficiently transports material to the clouds would require ocean:magma interactions or the subduction of a hydrated oceanic crust, neither of which occur on modern Venus. The transport of the erupted material to altitudes coinciding with the observations of phosphine is consequently very inefficient. Using the model proposed by Truong and Lunine as a base case, we estimate that an eruption volume of at least 21,600 km3/year would be required to explain the presence of 1 ppb phosphine in the clouds. This is greater than any historical terrestrial eruption rate, and would have several detectable consequences for remote and in situ observations to confirm. More realistic lithospheric mineralogy, volcano mechanics or atmospheric photochemistry require even more volcanism.

Recovery of Phosphine in Venus' Atmosphere from SOFIA Observations

“…The origins of any phosphine present are also debated, and most scenarios are hard to test for lack of some contextual data. For example, it seems only extreme volcanic activity could make ~ppb-level phosphine (Bains et al, 2022) but vulcanism on Venus is not well understood.…”

Venus, Phosphine and the Possibility of Life

“…Such an analysis was conducted in [58] where a wide range of chemical processes were examined to see if there is any potential source of phosphine in sufficient abundance to explain the observations with processes that we know are underway on the planet. The processes examined included gas reactions, geochemical reactions, photochemistry, volcanism (see also [59]), lightning and impactors. An example of the kind of chemical reaction network considered is shown in Figure 11, where the reaction rate and the destruction rates are compared.…”

“…For phosphine to be produced in significant amounts the whole reaction network must have this ratio ≥ 1 but, as can be seen, critical segments of the network have ratios orders of magnitudes less than this. More generally, it was found that the lifetime of free phosphine at various altitudes in the atmosphere of Venus ranged from < 1 second to perhaps a century [59], making it highly unlikely that a significant amount of phosphine can accumulate from any hypothetical source.…”

“…VERITAS and EnVISION are primarily concerned with the surface and interior of Venus, studying the history and role of volcanism on the planet. While they will doubtless reveal much that is of interest, they are unlikely to have much to say about phosphine and the processes underway in the clouds of Venus unless they uncover volcanic activity vastly in excess of our current understanding [59]. DAVINCI, however, is a much more interesting prospect.…”

Ammonia and Phosphine in the Clouds of Venus as Potentially Biological Anomalies

“…Finally, there have been some attempts to explain the presence of PH 3 on Venus through known abiotic chemistry [42,43]. So far, however, none of these attempts have been able to satisfactorily explain the presence of PH 3 , either because they do not predict enough PH 3 to explain the observations, especially above the clouds, or because they predict other molecules, especially water vapor, in large amounts that contradict observations [30,44,45]. Life using expected energy-metabolic pathways produce similar contradictions [46].…”